U.S. patent application number 16/996014 was filed with the patent office on 2021-02-25 for acoustic wave device with varying electrode pitch.
The applicant listed for this patent is SKYWORKS SOLUTIONS, INC.. Invention is credited to Rei Goto.
Application Number | 20210058060 16/996014 |
Document ID | / |
Family ID | 1000005033465 |
Filed Date | 2021-02-25 |
View All Diagrams
United States Patent
Application |
20210058060 |
Kind Code |
A1 |
Goto; Rei |
February 25, 2021 |
ACOUSTIC WAVE DEVICE WITH VARYING ELECTRODE PITCH
Abstract
A surface acoustic wave resonator comprises interdigital
transducer (IDT) electrodes disposed on an upper surface of a
piezoelectric substrate between first and second reflector gratings
each including reflector electrodes. The IDT electrodes include a
central region having a first width in a direction perpendicular to
an extension direction of the IDT electrodes and edge regions each
having a second width on opposite sides of the central region. The
IDT electrodes have a lesser average pitch in the central region
than an average pitch of the IDT electrodes in each of the edge
regions. The reflector electrodes have a lesser average pitch than
the average pitch of the IDT electrodes in the central region.
Inventors: |
Goto; Rei; (Osaka-Shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SKYWORKS SOLUTIONS, INC. |
Irvine |
CA |
US |
|
|
Family ID: |
1000005033465 |
Appl. No.: |
16/996014 |
Filed: |
August 18, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62890336 |
Aug 22, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03H 9/25 20130101; H03H
9/14582 20130101; H03H 9/6483 20130101; H03H 9/02842 20130101; H03H
9/02574 20130101; H03H 9/6406 20130101 |
International
Class: |
H03H 9/145 20060101
H03H009/145; H03H 9/64 20060101 H03H009/64; H03H 9/25 20060101
H03H009/25; H03H 9/02 20060101 H03H009/02 |
Claims
1. A surface acoustic wave (SAW) resonator comprising interdigital
transducer (IDT) electrodes disposed on an upper surface of a
piezoelectric substrate between first and second reflector gratings
each including reflector electrodes, the IDT electrodes including a
central region having a first width in a direction perpendicular to
an extension direction of the IDT electrodes and edge regions each
having a second width on opposite sides of the central region, the
IDT electrodes having a lesser average pitch in the central region
than an average pitch of the IDT electrodes in each of the edge
regions, the reflector electrodes having a lesser average pitch
than the average pitch of the IDT electrodes in the central
region.
2. The SAW resonator of claim 1 wherein the IDT electrodes have a
constant pitch throughout the central region.
3. The SAW resonator of claim 1 wherein the pitch of the IDT
electrodes in the edge regions increase with distance from the
central region.
4. The SAW resonator of claim 3 wherein the pitch of the IDT
electrodes in the edge regions increase monotonically with distance
from the central region.
5. The SAW resonator of claim 1 wherein the pitch of the IDT
electrodes in the edge regions increase with distance from the
central region, reach a maximum at a defined distance from the
central region, and then decrease from the defined distance from
the central region to outer edges of the edge regions.
6. The SAW resonator of claim 5 wherein the pitch of the IDT
electrodes at the outer edges of the edge regions is substantially
the same as the average pitch of the reflector electrodes.
7. The SAW resonator of claim 5 wherein the defined distance is at
least half of the second width.
8. The SAW resonator of claim 1 wherein the pitch of the IDT
electrodes abruptly increases at boundaries between the central
region and each edge region from a lesser pitch in the central
region to a greater pitch in each of the edge regions.
9. The SAW resonator of claim 8 wherein the pitch of the IDT
electrodes in the edge regions are constant across a portion of
each of the edge regions from the boundaries between the central
region and each edge region to defined distances from the
boundaries between the central region and each edge region.
10. The SAW resonator of claim 9 wherein the pitch of the IDT
electrodes in the edge regions decrease with distance from the
central region from the defined distances to outer edges of the
edge regions.
11. The SAW resonator of claim 10 wherein the pitch of the IDT
electrodes at the outer edges of the edge regions is substantially
the same as the average pitch of the reflector electrodes.
12. The SAW resonator of claim 9 wherein the defined distances are
at least half of the second width.
13. The SAW resonator of claim 1 wherein the pitch of the IDT
electrodes in the edge regions increase with distance from
boundaries between the central region and each edge region from a
lesser pitch in the central region to a greater pitch in each of
the edge regions and maintain a constant pitch from first distances
through the edge regions to second distances through the edge
regions.
14. The SAW resonator of claim 13 wherein the pitch of the IDT
electrodes in the edge regions decrease with distance from the
second distances to outer edges of the edge regions.
15. The SAW resonator of claim 14 wherein the pitch of the IDT
electrodes at the outer edges of the edge regions is substantially
the same as the average pitch of the reflector electrodes.
16. The SAW resonator of claim 1 free of any dielectric layer
disposed on the substrate, IDT electrodes, or reflector
electrodes.
17. The SAW resonator of claim 1 wherein the substrate is a
multilayer piezoelectric substrate including a layer of
piezoelectric material disposed above a layer of a material having
a higher impedance than the piezoelectric substrate.
18. The SAW resonator of claim 17 wherein the substrate further
includes a layer of silicon dioxide between the layer of
piezoelectric material and the layer of a material having the
higher impedance than the piezoelectric substrate.
19. An electronics module having at least one radio frequency
filter including at least one surface acoustic wave resonator
comprising interdigital transducer (IDT) electrodes disposed on an
upper surface of a piezoelectric substrate between first and second
reflector gratings each including reflector electrodes, the IDT
electrodes including a central region having a first width in a
direction perpendicular to an extension direction of the IDT
electrodes and edge regions each having a second width on opposite
sides of the central region, the IDT electrodes having a lesser
average pitch in the central region than an average pitch of the
IDT electrodes in each of the edge regions, the reflector
electrodes having a lesser average pitch than the average pitch of
the IDT electrodes in the central region.
20. An electronic device with an electronics module having at least
one radio frequency filter including at least one surface acoustic
wave resonator comprising interdigital transducer (IDT) electrodes
disposed on an upper surface of a piezoelectric substrate between
first and second reflector gratings each including reflector
electrodes, the IDT electrodes including a central region having a
first width in a direction perpendicular to an extension direction
of the IDT electrodes and edge regions each having a second width
on opposite sides of the central region, the IDT electrodes having
a lesser average pitch in the central region than an average pitch
of the IDT electrodes in each of the edge regions, the reflector
electrodes having a lesser average pitch than the average pitch of
the IDT electrodes in the central region.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.
119(e) to U.S. Provisional Patent Application No. 62/890,336,
titled ACOUSTIC WAVE DEVICE WITH VARYING ELECTRODE PITCH, filed
Aug. 22, 2019, the content of which being incorporated herein in
its entirety for all purposes.
BACKGROUND
Technical Field
[0002] Embodiments of this disclosure relate to acoustic wave
devices and the suppression of spurious signals in same.
Description of Related Technology
[0003] Acoustic wave devices, for example, surface acoustic wave
(SAW) and bulk acoustic wave (BAW) devices may be utilized as
components of filters in radio frequency electronic systems. For
instance, filters in a radio frequency front-end of a mobile phone
can include acoustic wave filters. Two acoustic wave filters can be
arranged as a duplexer or diplexer.
SUMMARY
[0004] In accordance with an aspect, there is provided a surface
acoustic wave (SAW) resonator comprising interdigital transducer
(IDT) electrodes disposed on an upper surface of a piezoelectric
substrate between first and second reflector gratings each
including reflector electrodes, the IDT electrodes including a
central region having a first width in a direction perpendicular to
an extension direction of the IDT electrodes and edge regions each
having a second width on opposite sides of the central region, the
IDT electrodes having a lesser average pitch in the central region
than an average pitch of the IDT electrodes in each of the edge
regions, the reflector electrodes having a lesser average pitch
than the average pitch of the IDT electrodes in the central
region.
[0005] In some embodiments, the IDT electrodes have a constant
pitch throughout the central region.
[0006] In some embodiments, the reflector electrodes have a
constant pitch.
[0007] In some embodiments, the pitch of the IDT electrodes in the
edge regions increase with distance from the central region. The
pitch of the IDT electrodes in the edge regions may increase
monotonically with distance from the central region.
[0008] In some embodiments, the pitch of the IDT electrodes in the
edge regions increase with distance from the central region, reach
a maximum at a defined distance from the central region, and then
decrease from the defined distance from the central region to outer
edges of the edge regions. The pitch of the IDT electrodes in the
edge regions may increase monotonically with distance from the
central region and monotonically decrease from the defined distance
from the central region to outer edges of the edge regions. The
pitch of the IDT electrodes at the outer edges of the edge regions
may be substantially the same as the average pitch of the reflector
electrodes. The defined distance may be at least half of the second
width.
[0009] In some embodiments, the pitch of the IDT electrodes
abruptly increases at boundaries between the central region and
each edge region from a lesser pitch in the central region to a
greater pitch in each of the edge regions.
[0010] In some embodiments, the pitch of the IDT electrodes in the
edge regions are constant across a portion of each of the edge
regions from the boundaries between the central region and each
edge region to defined distances from the boundaries between the
central region and each edge region.
[0011] In some embodiments, the pitch of the IDT electrodes in the
edge regions decrease with distance from the central region from
the defined distances to outer edges of the edge regions. The pitch
of the IDT electrodes in the edge regions may decrease
monotonically with distance from the central region from the
defined distances to outer edges of the edge regions.
[0012] In some embodiments, the pitch of the IDT electrodes at the
outer edges of the edge regions is substantially the same as the
average pitch of the reflector electrodes.
[0013] In some embodiments, the defined distances are at least half
of the second width.
[0014] In some embodiments, the pitch of the IDT electrodes in the
edge regions increase with distance from boundaries between the
central region and each edge region from a lesser pitch in the
central region to a greater pitch in each of the edge regions and
maintain a constant pitch from first distances through the edge
regions to second distances through the edge regions. The pitch of
the IDT electrodes in the edge regions may monotonically increase
with distance from the boundaries between the central region and
each edge region.
[0015] In some embodiments, the pitch of the IDT electrodes in the
edge regions decrease with distance from the second distances to
outer edges of the edge regions. The pitch of the IDT electrodes in
the edge regions may monotonically decrease with distance from the
second distances to outer edges of the edge regions.
[0016] In some embodiments, the pitch of the IDT electrodes at the
outer edges of the edge regions is substantially the same as the
average pitch of the reflector electrodes.
[0017] In some embodiments, the SAW resonator further comprises a
layer of silicon dioxide disposed on the substrate, IDT electrodes,
and reflector electrodes.
[0018] In some embodiments, the SAW resonator is free of any
dielectric layer disposed on the substrate, IDT electrodes, or
reflector electrodes.
[0019] In some embodiments, the substrate is a multilayer
piezoelectric substrate. The substrate may include a layer of
piezoelectric material disposed above a layer of a material having
a higher impedance than the piezoelectric substrate. The substrate
may further include a layer of silicon dioxide between the layer of
piezoelectric material and the layer of a material having the
higher impedance than the piezoelectric substrate
[0020] In accordance with another aspect, there is provided a radio
frequency filter including at least one surface acoustic wave
resonator comprising interdigital transducer (IDT) electrodes
disposed on an upper surface of a piezoelectric substrate between
first and second reflector gratings each including reflector
electrodes, the IDT electrodes including a central region having a
first width in a direction perpendicular to an extension direction
of the IDT electrodes and edge regions each having a second width
on opposite sides of the central region, the IDT electrodes having
a lesser average pitch in the central region than an average pitch
of the IDT electrodes in each of the edge regions, the reflector
electrodes having a lesser average pitch than the average pitch of
the IDT electrodes in the central region.
[0021] In accordance with another aspect, there is provided an
electronics module having at least one radio frequency filter
including at least one surface acoustic wave resonator comprising
interdigital transducer (IDT) electrodes disposed on an upper
surface of a piezoelectric substrate between first and second
reflector gratings each including reflector electrodes, the IDT
electrodes including a central region having a first width in a
direction perpendicular to an extension direction of the IDT
electrodes and edge regions each having a second width on opposite
sides of the central region, the IDT electrodes having a lesser
average pitch in the central region than an average pitch of the
IDT electrodes in each of the edge regions, the reflector
electrodes having a lesser average pitch than the average pitch of
the IDT electrodes in the central region.
[0022] In accordance with another aspect, there is provided an
electronic device with an electronics module having at least one
radio frequency filter including at least one surface acoustic wave
resonator comprising interdigital transducer (IDT) electrodes
disposed on an upper surface of a piezoelectric substrate between
first and second reflector gratings each including reflector
electrodes, the IDT electrodes including a central region having a
first width in a direction perpendicular to an extension direction
of the IDT electrodes and edge regions each having a second width
on opposite sides of the central region, the IDT electrodes having
a lesser average pitch in the central region than an average pitch
of the IDT electrodes in each of the edge regions, the reflector
electrodes having a lesser average pitch than the average pitch of
the IDT electrodes in the central region.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Embodiments of this disclosure will now be described, by way
of non-limiting example, with reference to the accompanying
drawings.
[0024] FIG. 1A is a simplified plan view of an example of a surface
acoustic wave resonator;
[0025] FIG. 1B is a simplified plan view of another example of a
surface acoustic wave resonator;
[0026] FIG. 1C is a simplified plan view of another example of a
surface acoustic wave resonator;
[0027] FIG. 2A is a simplified cross-sectional view of a portion of
an example of a surface acoustic wave resonator;
[0028] FIG. 2B is a simplified cross-sectional view of a portion of
another example of a surface acoustic wave resonator;
[0029] FIG. 2C is a simplified cross-sectional view of a portion of
another example of a surface acoustic wave resonator;
[0030] FIG. 2D is a simplified cross-sectional view of a portion of
another example of a surface acoustic wave resonator;
[0031] FIG. 2E is a simplified cross-sectional view of a portion of
another example of a surface acoustic wave resonator;
[0032] FIG. 2F is a simplified cross-sectional view of a portion of
another example of a surface acoustic wave resonator;
[0033] FIG. 3A is a dispersion diagram of an example of a surface
acoustic wave resonator;
[0034] FIG. 3B is a passband of a ladder filter formed from surface
acoustic wave resonators having the dispersion diagram of FIG.
3A;
[0035] FIG. 3C is a dispersion diagram of another example of a
surface acoustic wave resonator;
[0036] FIG. 3D is a passband of a ladder filter formed from surface
acoustic wave resonators having the dispersion diagram of FIG.
3C;
[0037] FIG. 4 illustrates how dispersion diagrams of examples of
surface acoustic wave resonators change with changes in silicon
dioxide layer thickness;
[0038] FIG. 5A illustrates resonator performance characteristics of
a resonator having a dispersion diagram as illustrated in FIG.
3A;
[0039] FIG. 5B illustrates resonator performance characteristics of
a resonator having a dispersion diagram as illustrated in FIG.
3B;
[0040] FIG. 6 illustrates an example of a SAW resonator with
different electrode pitches in different portions of the
resonator;
[0041] FIG. 7 illustrates the passband of a ladder filter formed of
resonators as illustrated in FIG. 6 as compared to the passband of
a ladder filter formed of resonators having a constant electrode
pitch throughout;
[0042] FIG. 8 illustrates another example of a SAW resonator with
different electrode pitches in different portions of the
resonator;
[0043] FIG. 9A illustrates another example of a SAW resonator with
different electrode pitches in different portions of the
resonator;
[0044] FIG. 9B illustrates another example of a SAW resonator with
different electrode pitches in different portions of the
resonator;
[0045] FIG. 10 illustrates another example of a SAW resonator with
different electrode pitches in different portions of the
resonator;
[0046] FIG. 11 is a schematic diagram of a radio frequency ladder
filter;
[0047] FIG. 12 is a block diagram of one example of a filter module
that can include one or more acoustic wave elements according to
aspects of the present disclosure;
[0048] FIG. 13 is a block diagram of one example of a front-end
module that can include one or more filter modules according to
aspects of the present disclosure; and
[0049] FIG. 14 is a block diagram of one example of a wireless
device including the front-end module of FIG. 13.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0050] The following description of certain embodiments presents
various descriptions of specific embodiments. However, the
innovations described herein can be embodied in a multitude of
different ways, for example, as defined and covered by the claims.
In this description, reference is made to the drawings where like
reference numerals can indicate identical or functionally similar
elements. It will be understood that elements illustrated in the
figures are not necessarily drawn to scale. Moreover, it will be
understood that certain embodiments can include more elements than
illustrated in a drawing and/or a subset of the elements
illustrated in a drawing. Further, some embodiments can incorporate
any suitable combination of features from two or more drawings.
[0051] FIG. 1A is a plan view of a surface acoustic wave (SAW)
resonator 10 such as might be used in a SAW filter, duplexer,
balun, etc.
[0052] Acoustic wave resonator 10 is formed on a piezoelectric
substrate, for example, a lithium tantalate (LiTaO.sub.3, "LT") or
lithium niobate (LiNbO.sub.3, "LN") substrate 12 and includes
Interdigital Transducer (IDT) electrodes 14 and reflector
electrodes 16. In use, the IDT electrodes 14 excite a main acoustic
wave having a wavelength .lamda. along a surface of the
piezoelectric substrate 12. The reflector electrodes 16 sandwich
the IDT electrodes 14 and reflect the main acoustic wave back and
forth through the IDT electrodes 14. The main acoustic wave of the
device travels perpendicular to the lengthwise direction of the IDT
electrodes.
[0053] The IDT electrodes 14 include a first bus bar electrode 18A
and a second bus bar electrode 18B facing first bus bar electrode
18A. The IDT electrodes 14 further include first electrode fingers
20A extending from the first bus bar electrode 18A toward the
second bus bar electrode 18B, and second electrode fingers 20B
extending from the second bus bar electrode 18B toward the first
bus bar electrode 18A.
[0054] The reflector electrodes 16 (also referred to as reflector
gratings) each include a first reflector bus bar electrode 24A and
a second reflector bus bar electrode 24B and reflector fingers 26
extending between and electrically coupling the first bus bar
electrode 24A and the second bus bar electrode 24B.
[0055] In other embodiments disclosed herein, as illustrated in
FIG. 1B, the reflector bus bar electrodes 24A, 24B may be omitted
and the reflector fingers 26 may be electrically unconnected.
Further, as illustrated in FIG. 1C, acoustic wave resonators as
disclosed herein may include dummy electrode fingers 20C that are
aligned with respective electrode fingers 20A, 20B. Each dummy
electrode finger 20C extends from the opposite bus bar electrode
18A, 18B than the respective electrode finger 20A, 20B with which
it is aligned.
[0056] It should be appreciated that the acoustic wave resonators
10 illustrated in FIGS. 1A-1C, as well as the other circuit
elements illustrated in other figures presented herein, are
illustrated in a highly simplified form. The relative dimensions of
the different features are not shown to scale. Further, typical
acoustic wave resonators would commonly include a far greater
number of electrode fingers and reflector fingers than illustrated.
Typical acoustic wave resonators or filter elements may also
include multiple IDT electrodes sandwiched between the reflector
electrodes.
[0057] Different SAW resonator designs may include different
substrate structures and may or may not include a layer of
dielectric material covering the substrates and IDT electrodes.
FIG. 2A is a partial cross-sectional view representative of one
class of SAW resonator designs. The design of FIG. 2A includes IDT
electrodes 20 and reflector electrodes 26 disposed on a substrate
12 formed of a layer of piezoelectric material 30, for example, LN
as illustrated in FIG. 2A.
[0058] An example of another class of SAW resonator designs is
illustrated in partial cross-sectional view in FIG. 2B. The SAW
resonator design of FIG. 2B includes a multi-layer piezoelectric
substrate (MPS) in which a layer of piezoelectric material 30 is
disposed on the top of a layer of a high impedance material 32, for
example, silicon, aluminum nitride, silicon nitride, magnesium
oxide spinel, magnesium oxide crystal, sapphire, or another
suitable high impedance material. The layer of high impedance
material may increase the mechanical robustness of the
piezoelectric substrate during fabrication of SAW resonators on the
substrate and increase manufacturing yield, reduce the amount by
which operating parameters of the SAW resonators formed on the
piezoelectric substrate change with temperature during operation,
for example, by reducing the temperature coefficient of frequency
of the substrate as compared to a substrate formed of piezoelectric
material only, and/or improve the thermal conductivity of the
substrate as compared to a substrate formed of piezoelectric
material only, which may facilitate cooling and help prevent
overheating of the SAW resonator. The high impedance material may
have a lower coefficient of linear expansion than the piezoelectric
material and a MPS substrate as illustrated in FIG. 2B may exhibit
a lesser change dimensions with changes in temperature than a
substrate including the piezoelectric material alone. The layer of
piezoelectric material 30 may be at least 0.1.lamda. thick, for
example between 0.1.lamda. and 5.lamda., thick, while the layer of
high impedance material 32 may be thicker, for example, up to about
500 .mu.m thick.
[0059] The layer of high impedance material 32 may be provided in
the form of a wafer that is bonded to the lower surface of a wafer
of piezoelectric material opposite the upper surface of the wafer
of piezoelectric material upon which features of SAW resonators,
such as IDT electrodes and reflector electrodes, as well as other
circuitry, for example, conductive traces, passive devices, etc.,
may be formed. The layer of high impedance material 32 may be
bonded to the piezoelectric material via a direct fusion bond or
with an adhesive layer, for example, a thin layer of silicon
dioxide. In some embodiments, a layer of silicon dioxide may be
grown or deposited on the lower surface of the piezoelectric
material and a layer of silicon dioxide may be grown or deposited
on the upper surface of the layer of high impedance material 32.
The piezoelectric material and layer of high impedance material 32
may then be joined by anodic bonding or other methods of joining
layers of silicon dioxide known in the art.
[0060] The layer of high impedance material 32 may be a continuous
layer. The layer of high impedance material 32 may be present on
the lower surface of the piezoelectric material layer under all
areas where SAW resonators and/or additional circuitry is formed on
the piezoelectric material layer.
[0061] FIG. 2C illustrates another example of a class of SAW
resonator designs which is also a MPS substrate as illustrated in
FIG. 2B but further includes a layer of dielectric material 34
disposed between the piezoelectric material layer 30 and the layer
of high impedance material 32. The layer of dielectric material 34
may include or consist of silicon dioxide (SiO.sub.2). The
SiO.sub.2 layer 34 may have a negative temperature coefficient of
frequency, which helps to offset the positive temperature
coefficient of frequency of the piezoelectric material and reduce
the change in frequency response of the SAW device with changes in
temperature.
[0062] Any of the structures illustrated in FIGS. 2A-2C may further
include a layer of dielectric material 36 formed on the upper
surface of the substrate and IDT and reflector electrodes. Examples
of these structures are illustrated in FIGS. 2D-2F, respectively.
The layer of dielectric material 36 may include or consist of
SiO.sub.2 or may be a multilayer dielectric including a layer of
SiO.sub.2 covered partially or wholly by another dielectric
material, for example, silicon nitride (Si.sub.3N.sub.4, "SiN").
The dielectric material layer 36 may have a negative temperature
coefficient of frequency, which helps to offset the positive
temperature coefficient of frequency of the piezoelectric material
and reduce the change in frequency response of the SAW device with
changes in temperature. A SAW device with a layer of SiO.sub.2 over
the piezoelectric material layer 30 and IDT electrodes may thus be
referred to as a temperature-compensated SAW device, or TCSAW.
[0063] Examples of SAW resonators including a layer of SiO.sub.2
disposed on top of a piezoelectric substrate, for example, as
illustrated in FIG. 2D, and having IDT electrodes and reflector
electrode spaced with a constant pitch may exhibit a dispersion
diagram as illustrated in FIG. 3A, in which f.sub.s is the series
resonance frequency and f.sub.p is the parallel or anti-resonance
frequency. In FIG. 3A the vertical axis represents wave number
(which is related to IDT electrode pitch) and the horizontal axis
represents frequency. This dispersion curve is defined under the
conditions of the open grating and short gratings. In the stop band
of the dispersion curve, complex components appear. For example, a
dispersion diagram as illustrated in FIG. 3A may be a case where
the stop band of the open grating is included in the stop band of
the short grating and also the upper end of the stop band of the
open grating coincides with the upper end of the stop band of the
short grating. A ladder filter formed under these conditions may
exhibit a "well-behaved" flat passband curve, for example as
illustrated in FIG. 3B. In contrast, examples of SAW resonators not
including a layer of SiO.sub.2 disposed on top of a piezoelectric
substrate, for example, as illustrated in FIG. 2A, and having IDT
electrodes and reflector electrode spaced with a constant pitch may
exhibit a dispersion diagram as illustrated in FIG. 3C in which the
short grating stop band does not completely include the open
grating stop band. A filter, for example, a RF ladder filter formed
from SAW resonators exhibiting a dispersion curve as illustrated in
FIG. 3C may exhibit a passband curve that is degraded and includes
multiple ripples or departures from flatness as illustrated in FIG.
3D.
[0064] When a near 128 degree rotated Y cut X propagation lithium
niobate substrate is used as a piezoelectric substrate, the amount
of silicon dioxide covering a substrate of a SAW resonator may
determine whether the short grating stop band of the resonator
includes the open grating stop band or not. For example, as
illustrated in FIG. 4, for an example of a SAW resonator structure,
the short grating stop band of the resonator includes the open
grating stop band when the silicon dioxide thickness is at least
0.15.lamda.. The short grating stop band of the resonator does not
include the open grating stop band when the silicon dioxide
thickness is less than 0.15.lamda..
[0065] FIGS. 5A and 5B illustrates admittance and quality factor Q
curves associated with SAW resonators exhibiting dispersion
diagrams as illustrated in FIGS. 3A and 3C, respectively. From
FIGS. 5A and 5B it can be seen that for SAW resonators having
dispersion curves in which the short grating stop band includes the
open grating stop band as illustrated in FIG. 3A, the short grating
stop band includes both the resonant and anti-resonant frequencies
of the resonator and the resonator exhibits desirable smooth
admittance and quality factor curves. In contrast for SAW
resonators having dispersion curves in which the short grating stop
band does not include the open grating stop band as illustrated in
FIG. 3C, the short grating stop band does not include both the
resonant and anti-resonant frequencies of the resonator and the
resonator exhibits undesirable unsmooth admittance and quality
factor curves.
[0066] It has been discovered that in RF filters including SAW
resonator designs that might exhibit degraded passband
characteristics, for example, as illustrated in FIG. 3D, the
passband characteristics, e.g., the flatness of the passband may be
improved by making changes to the pitch of the IDT electrodes in
certain regions of the SAW resonators of the filter and/or by
making changes to the pitch of the reflector electrodes of the SAW
resonators. One example of such a modification to the pitch of the
electrodes of a SAW resonator is illustrated in FIG. 6. As
illustrated, the SAW resonator of FIG. 6 includes IDT electrodes
with a central region with constant electrode pitch, indicated as
"IDT main pitch" in FIG. 6. Opposite edge regions of the IDT
electrodes include IDT electrodes with average pitches greater than
the IDT main pitch of the IDT electrodes in the central region. In
some embodiments, the edge regions may be from about 5.lamda., to
about 10.lamda., wide and the central region may be greater than
10.lamda., or greater than 30.lamda. or 50.lamda. wide. The pitches
of the IDT electrodes in the edge regions are indicated as "IDT
edge pitch" in FIG. 6 and are greater than the IDT main pitch of
the IDT electrodes in the central region. The average pitches of
the IDT electrodes in the edge regions are greater than the average
IDT main pitch of the IDT electrodes in the central region. The
pitch of the IDT electrodes in the edge regions may increase
monotonically from edges of the central region to outside edges of
the edge regions as indicated in FIG. 6. The pitch of the IDT
electrodes in the edge region may increase to between about 5% to
about 20% greater, for example, about 10% greater, than the IDT
main pitch of the IDT electrodes in the central region. In
contrast, the pitch of the reflector electrodes, indicated as
"reflector pitch" in FIG. 6, is reduced to a value or an average
value below that of the IDT main pitch of the IDT electrodes in the
central region of IDT electrodes of the resonator. The pitch of the
reflector electrodes may be constant across the width of the
reflectors and may be about 3% to about 4% less or up to about 10%
less than the pitch of the IDT main pitch of the IDT electrodes in
the central region of the IDT electrodes.
[0067] The improvement in flatness of the passband of an RF filter
including resonators including the modification to the electrode
pitches as illustrated in FIG. 6 as compared to the passband of a
similar RF filter including SAW resonators as illustrated in FIG. 6
with a baseline constant electrode pitch for all the IDT electrodes
and reflector electrodes is illustrated in FIG. 7. It can be seen
that the modification to the electrode pitches significantly
improves the flatness of the passband from the "baseline" curve to
the "revised" curve.
[0068] In other embodiments, the change in electrode pitch may have
different profiles than illustrated in FIG. 6. An additional
example, illustrated in FIG. 8, includes IDT electrodes in the edge
regions with pitches that first monotonically increase with
distance from the central region, reach a peak within the edge
region, for example, at a point more than halfway, about 75%, about
80%, or about 90% through the widths of the edge regions, and then
monotonically decrease within the edge regions with further
distance from the central region until the pitches reach the lower
value of the reflector electrode pitch at the outer edges of the
edge regions. The pitch of the IDT electrodes in the edge region
may increase to between about 5% to about 20% greater, for example,
about 10% greater than the IDT main pitch of the IDT electrodes in
the central region. The pitches of the IDT electrodes in the edge
regions may have an average pitch greater than the IDT main pitch
of the IDT electrodes in the central region. The electrode pitch in
the reflectors is constant and may be about 3% to about 4% less or
up to about 10% less than the pitch of the IDT main pitch of the
IDT electrodes in the central region of the IDT electrodes.
[0069] A further example, illustrated in FIG. 9A, includes IDT
electrodes with a constant IDT main pitch in the central region of
the IDT electrodes. The pitch of the IDT electrodes increases
immediately from the IDT main pitch to the IDT edge pitches at the
boundary between the central region and each edge region. The pitch
of the IDT electrodes in the edge regions maintains a constant IDT
edge pitch through portions of the edge regions with distance from
the central region. Beginning at points in the edge regions, for
example, more than halfway, about 75%, about 80%, or about 90%
through the widths of the edge regions from the central regions,
the pitch of the IDT electrodes monotonically decrease within the
edge regions with further distance from the central region until
the pitches reach the lower value of the reflector electrode pitch
at the outer edges of the edge regions. The pitch of the IDT
electrodes in the edge region may increase to between about 5% to
about 20% greater, for example, about 10% greater, than the IDT
main pitch of the IDT electrodes in the central region. The pitches
of the IDT electrodes in the edge regions may have an average pitch
greater than the IDT main pitch of the IDT electrodes in the
central region. The electrode pitch in the reflectors is constant
and may be about 3% to about 4% less or up to about 10% less than
the pitch of the IDT main pitch of the IDT electrodes in the
central region of the IDT electrodes. In a variation of the SAW
resonator illustrated in FIG. 9A, the IDT edge pitch may be
constant throughout the edge regions as illustrated in FIG. 9B.
[0070] In another example, illustrated in FIG. 10, the SAW
resonator includes IDT electrodes with a constant IDT main pitch in
the central region of the IDT electrodes. The pitch of the IDT
electrodes first monotonically increases in the edge regions
beginning at the inner edges of the edge regions with increasing
distance from the central region. The pitch of the IDT electrodes
in the edge regions achieves a maximum value at a first distance
into the edge regions, for example, about 5%, about 10%, or about
25% into the edge regions, and then maintains a constant IDT edge
pitch through portions of the edge regions with additional distance
from the central region. Beginning at a second distance in the edge
regions, for example, more than halfway or about 75%, about 80%, or
about 90% through the widths of the edge regions from the central
regions, the pitch of the IDT electrodes monotonically decrease
within the edge regions with further distance from the central
region until the pitches reach the lower value of the reflector
electrode pitch at the outer edges of the edge regions. The pitch
of the IDT electrodes in the edge region may increase to between
about 5% to about 20% greater, for example, about 10% greater, than
the IDT main pitch of the IDT electrodes in the central region. The
pitches of the IDT electrodes in the edge regions may have an
average pitch greater than the IDT main pitch of the IDT electrodes
in the central region. The electrode pitch in the reflectors is
constant and may be about 3% to about 4% less or up to about 10%
less than the pitch of the IDT main pitch of the IDT electrodes in
the central region of the IDT electrodes.
[0071] It should be appreciated that the change in pitch of the IDT
electrodes in the edge regions as illustrated in the embodiments of
FIGS. 6, 8, 9A, 9B, and 10 need not be monotonic as illustrated,
but in other embodiments may change with a curved profile. In other
embodiments, the embodiments illustrated in FIGS. 9A, 9B, and 10
may be modified such that the profile of IDT electrode pitch in the
edge regions need not have flat tops, but, additionally or
alternatively, may have curved upper portions.
[0072] Each of the examples illustrated in FIGS. 6, 8, 9A, 9B, and
10 has a reflector pitch that is less than a main pitch of the IDT
electrodes in the central region and an edge pitch in at least a
portion of the edge regions of the IDT electrodes that is greater
than the main pitch of the IDT electrodes in the central region.
Also, each of the examples illustrated in FIGS. 6, 8, 9A, 9B, and
10 has IDT electrodes having a lesser average pitch in the central
region than an average pitch of the IDT electrodes in each of the
edge regions and reflector electrodes having a lesser average pitch
than the average pitch of the IDT electrodes in the central region.
Further, as illustrated in the examples of FIGS. 8, 9A, and 10, in
some embodiments, the pitch of the IDT electrodes at the outer
edges of the edge regions may be substantially the same as the
pitch or average pitch of the reflector electrodes. Each of the
examples illustrated in FIGS. 6, 8, 9A, 9B, and 10 include
reflectors with bus bars and reflector electrode fingers extending
between the bus bars. In other examples, SAW resonators having
electrode pitch configurations similar to or substantially the same
as those illustrated in FIGS. 6, 8, 9A, 9B, and 10 may include
reflectors without bus bars wherein the reflector electrode fingers
are electrically unconnected, for example, as illustrated in FIG.
1B.
[0073] Electrode pitch profiles as described herein may be
applicable to SAW resonators or filters having substrates without a
SiO.sub.2 upper layer covering the electrodes and substrate, for
example, as illustrated in FIGS. 2A-2C, but may also be utilized in
SAW resonators or filter devices including a SiO.sub.2 upper layer
covering the electrodes and substrate, for example, as illustrated
in FIGS. 2D-2F, as well as with SAW resonators or filter devices
including other substrate configurations known in the art.
[0074] In some embodiments, multiple SAW resonators as disclosed
herein may be combined into a filter, for example, an RF ladder
filter schematically illustrated in FIG. 11 and including a
plurality of series resonators R1, R3, R5, R7, and R9, and a
plurality of parallel (or shunt) resonators R2, R4, R6, and R8. As
shown, the plurality of series resonators R1, R3, R5, R7, and R9
are connected in series between the input and the output of the RF
ladder filter, and the plurality of parallel resonators R2, R4, R6,
and R8 are respectively connected between series resonators and
ground in a shunt configuration. Other filter structures and other
circuit structures known in the art that may include SAW devices or
resonators, for example, duplexers, baluns, etc., may also be
formed including examples of SAW resonators as disclosed
herein.
[0075] Examples of the SAW devices, e.g., SAW resonators discussed
herein can be implemented in a variety of packaged modules. Some
example packaged modules will now be discussed in which any
suitable principles and advantages of the SAW devices discussed
herein can be implemented. FIGS. 12, 13, and 14 are schematic block
diagrams of illustrative packaged modules and devices according to
certain embodiments.
[0076] As discussed above, surface acoustic wave resonators can be
used in surface acoustic wave (SAW) RF filters. In turn, a SAW RF
filter using one or more surface acoustic wave elements may be
incorporated into and packaged as a module that may ultimately be
used in an electronic device, such as a wireless communications
device, for example. FIG. 12 is a block diagram illustrating one
example of a module 315 including a SAW filter 300. The SAW filter
300 may be implemented on one or more die(s) 325 including one or
more connection pads 322. For example, the SAW filter 300 may
include a connection pad 322 that corresponds to an input contact
for the SAW filter and another connection pad 322 that corresponds
to an output contact for the SAW filter. The packaged module 315
includes a packaging substrate 330 that is configured to receive a
plurality of components, including the die 325. A plurality of
connection pads 332 can be disposed on the packaging substrate 330,
and the various connection pads 322 of the SAW filter die 325 can
be connected to the connection pads 332 on the packaging substrate
330 via electrical connectors 334, which can be solder bumps or
wirebonds, for example, to allow for passing of various signals to
and from the SAW filter 300. The module 315 may optionally further
include other circuitry die 340, for example, one or more
additional filter(s), amplifiers, pre-filters, modulators,
demodulators, down converters, and the like, as would be known to
one of skill in the art of semiconductor fabrication in view of the
disclosure herein. In some embodiments, the module 315 can also
include one or more packaging structures to, for example, provide
protection and facilitate easier handling of the module 315. Such a
packaging structure can include an overmold formed over the
packaging substrate 330 and dimensioned to substantially
encapsulate the various circuits and components thereon.
[0077] Various examples and embodiments of the SAW filter 300 can
be used in a wide variety of electronic devices. For example, the
SAW filter 300 can be used in an antenna duplexer, which itself can
be incorporated into a variety of electronic devices, such as RF
front-end modules and communication devices.
[0078] Referring to FIG. 13, there is illustrated a block diagram
of one example of a front-end module 400, which may be used in an
electronic device such as a wireless communications device (e.g., a
mobile phone) for example. The front-end module 400 includes an
antenna duplexer 410 having a common node 402, an input node 404,
and an output node 406. An antenna 510 is connected to the common
node 402.
[0079] The antenna duplexer 410 may include one or more
transmission filters 412 connected between the input node 404 and
the common node 402, and one or more reception filters 414
connected between the common node 402 and the output node 406. The
passband(s) of the transmission filter(s) are different from the
passband(s) of the reception filters. Examples of the SAW filter
300 can be used to form the transmission filter(s) 412 and/or the
reception filter(s) 414. An inductor or other matching component
420 may be connected at the common node 402.
[0080] The front-end module 400 further includes a transmitter
circuit 432 connected to the input node 404 of the duplexer 410 and
a receiver circuit 434 connected to the output node 406 of the
duplexer 410. The transmitter circuit 432 can generate signals for
transmission via the antenna 510, and the receiver circuit 434 can
receive and process signals received via the antenna 510. In some
embodiments, the receiver and transmitter circuits are implemented
as separate components, as shown in FIG. 13, however, in other
embodiments these components may be integrated into a common
transceiver circuit or module. As will be appreciated by those
skilled in the art, the front-end module 400 may include other
components that are not illustrated in FIG. 13 including, but not
limited to, switches, electromagnetic couplers, amplifiers,
processors, and the like.
[0081] FIG. 14 is a block diagram of one example of a wireless
device 500 including the antenna duplexer 410 shown in FIG. 13. The
wireless device 500 can be a cellular phone, smart phone, tablet,
modem, communication network or any other portable or non-portable
device configured for voice or data communication. The wireless
device 500 can receive and transmit signals from the antenna 510.
The wireless device includes an embodiment of a front-end module
400 similar to that discussed above with reference to FIG. 13. The
front-end module 400 includes the duplexer 410, as discussed above.
In the example shown in FIG. 14 the front-end module 400 further
includes an antenna switch 440, which can be configured to switch
between different frequency bands or modes, such as transmit and
receive modes, for example. In the example illustrated in FIG. 14,
the antenna switch 440 is positioned between the duplexer 410 and
the antenna 510; however, in other examples the duplexer 410 can be
positioned between the antenna switch 440 and the antenna 510. In
other examples the antenna switch 440 and the duplexer 410 can be
integrated into a single component.
[0082] The front-end module 400 includes a transceiver 430 that is
configured to generate signals for transmission or to process
received signals. The transceiver 430 can include the transmitter
circuit 432, which can be connected to the input node 404 of the
duplexer 410, and the receiver circuit 434, which can be connected
to the output node 406 of the duplexer 410, as shown in the example
of FIG. 13.
[0083] Signals generated for transmission by the transmitter
circuit 432 are received by a power amplifier (PA) module 450,
which amplifies the generated signals from the transceiver 430. The
power amplifier module 450 can include one or more power
amplifiers. The power amplifier module 450 can be used to amplify a
wide variety of RF or other frequency-band transmission signals.
For example, the power amplifier module 450 can receive an enable
signal that can be used to pulse the output of the power amplifier
to aid in transmitting a wireless local area network (WLAN) signal
or any other suitable pulsed signal. The power amplifier module 450
can be configured to amplify any of a variety of types of signal,
including, for example, a Global System for Mobile (GSM) signal, a
code division multiple access (CDMA) signal, a W-CDMA signal, a
Long-Term Evolution (LTE) signal, or an EDGE signal. In certain
embodiments, the power amplifier module 450 and associated
components including switches and the like can be fabricated on
gallium arsenide (GaAs) substrates using, for example,
high-electron mobility transistors (pHEMT) or insulated-gate
bipolar transistors (BiFET), or on a silicon substrate using
complementary metal-oxide semiconductor (CMOS) field effect
transistors.
[0084] Still referring to FIG. 14, the front-end module 400 may
further include a low noise amplifier module 460, which amplifies
received signals from the antenna 510 and provides the amplified
signals to the receiver circuit 434 of the transceiver 430.
[0085] The wireless device 500 of FIG. 14 further includes a power
management sub-system 520 that is connected to the transceiver 430
and manages the power for the operation of the wireless device 500.
The power management system 520 can also control the operation of a
baseband sub-system 530 and various other components of the
wireless device 500. The power management system 520 can include,
or can be connected to, a battery (not shown) that supplies power
for the various components of the wireless device 500. The power
management system 520 can further include one or more processors or
controllers that can control the transmission of signals, for
example. In one embodiment, the baseband sub-system 530 is
connected to a user interface 540 to facilitate various input and
output of voice and/or data provided to and received from the user.
The baseband sub-system 530 can also be connected to memory 550
that is configured to store data and/or instructions to facilitate
the operation of the wireless device, and/or to provide storage of
information for the user. Any of the embodiments described above
can be implemented in association with mobile devices such as
cellular handsets. The principles and advantages of the embodiments
can be used for any systems or apparatus, such as any uplink
wireless communication device, that could benefit from any of the
embodiments described herein. The teachings herein are applicable
to a variety of systems. Although this disclosure includes some
example embodiments, the teachings described herein can be applied
to a variety of structures. Any of the principles and advantages
discussed herein can be implemented in association with RF circuits
configured to process signals in a range from about 30 kHz to 5
GHz, such as in a range from about 600 MHz to 2.7 GHz.
[0086] Aspects of this disclosure can be implemented in various
electronic devices. Examples of the electronic devices can include,
but are not limited to, consumer electronic products, parts of the
consumer electronic products such as packaged radio frequency
modules, uplink wireless communication devices, wireless
communication infrastructure, electronic test equipment, etc.
Examples of the electronic devices can include, but are not limited
to, a mobile phone such as a smart phone, a wearable computing
device such as a smart watch or an ear piece, a telephone, a
television, a computer monitor, a computer, a modem, a hand-held
computer, a laptop computer, a tablet computer, a microwave, a
refrigerator, a vehicular electronics system such as an automotive
electronics system, a stereo system, a digital music player, a
radio, a camera such as a digital camera, a portable memory chip, a
washer, a dryer, a washer/dryer, a copier, a facsimile machine, a
scanner, a multi-functional peripheral device, a wrist watch, a
clock, etc. Further, the electronic devices can include unfinished
products.
[0087] Unless the context clearly requires otherwise, throughout
the description and the claims, the words "comprise," "comprising,"
"include," "including" and the like are to be construed in an
inclusive sense, as opposed to an exclusive or exhaustive sense;
that is to say, in the sense of "including, but not limited to."
The word "coupled", as generally used herein, refers to two or more
elements that may be either directly connected, or connected by way
of one or more intermediate elements. Likewise, the word
"connected", as generally used herein, refers to two or more
elements that may be either directly connected, or connected by way
of one or more intermediate elements. Additionally, the words
"herein," "above," "below," and words of similar import, when used
in this application, shall refer to this application as a whole and
not to any particular portions of this application. Where the
context permits, words in the above Detailed Description using the
singular or plural number may also include the plural or singular
number respectively. The word "or" in reference to a list of two or
more items, that word covers all of the following interpretations
of the word: any of the items in the list, all of the items in the
list, and any combination of the items in the list.
[0088] Moreover, conditional language used herein, such as, among
others, "can," "could," "might," "may," "e.g.," "for example,"
"such as" and the like, unless specifically stated otherwise, or
otherwise understood within the context as used, is generally
intended to convey that certain embodiments include, while other
embodiments do not include, certain features, elements and/or
states. Thus, such conditional language is not generally intended
to imply that features, elements and/or states are in any way
required for one or more embodiments or that one or more
embodiments necessarily include logic for deciding, with or without
author input or prompting, whether these features, elements and/or
states are included or are to be performed in any particular
embodiment.
[0089] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the disclosure. Indeed, the novel
apparatus, methods, and systems described herein may be embodied in
a variety of other forms; furthermore, various omissions,
substitutions and changes in the form of the methods and systems
described herein may be made without departing from the spirit of
the disclosure. For example, while blocks are presented in a given
arrangement, alternative embodiments may perform similar
functionalities with different components and/or circuit
topologies, and some blocks may be deleted, moved, added,
subdivided, combined, and/or modified. Each of these blocks may be
implemented in a variety of different ways. Any suitable
combination of the elements and acts of the various embodiments
described above can be combined to provide further embodiments. The
accompanying claims and their equivalents are intended to cover
such forms or modifications as would fall within the scope and
spirit of the disclosure.
* * * * *